Data and R code for: An experimental approach to assessing the impact of ecosystem engineers on biodiversity and ecosystem functions

Plants acting as ecosystem engineers create habitats and facilitate
biodiversity maintenance within plant communities. Furthermore,
biodiversity research has demonstrated that plant diversity enhances the
productivity and functioning of ecosystems. However, these two fields of
research developed in parallel and independent from one another, with the
consequence that little is known about the role of ecosystem engineers in
the relationship between biodiversity and ecosystem functioning across
trophic levels. Here, we present an experimental framework to study this
relationship. We combine facilitation by plants acting as ecosystem
engineers with plant–insect interaction analysis and variance partitioning
of biodiversity effects. We present a case-study experiment in which
facilitation by a cushion-plant species and a dwarf-shrub species as
ecosystem engineers increases positive effects of plant functional
diversity (ecosystem engineers and associated plants) on ecosystem
functioning (flower visitation rate). The experiment, conducted in the
field during a single alpine flowering season, included
the following treatments: 1) removal of plant species associated with
ecosystem engineers, 2) exclusion (covering) of ecosystem engineer
flowers, and 3) control, i.e. natural patches of ecosystem engineers and
associated plant species. We found both positive and negative
associational effects between plants depending on ecosystem engineer
identity, indicating both pollination facilitation and interference. In
both cases patches supported by ecosystem engineers increased phylogenetic
and functional diversity of flower visitors. Furthermore, complementarity
effects between engineers and associated plants were positive for flower
visitation rates. Our study reveals that plant facilitation can enhance
the strength of biodiversity–ecosystem functioning relationships, with
complementarity between plants for attracting more and diverse flower
visitors being the likely driver. A potential mechanism is that synergy
and complementarity between engineers and associated plants increase
attractiveness for shared visitors and widen pollination niches. In
synthesis, facilitation among plants can scale up to a full network,
supporting ecosystem functioning both directly via microhabitat
amelioration and indirectly via diversity effects.